The invention relates generally to the electrical, electronic and computer arts, and, more particularly, to post-production methods for customizing connections of conductors of a printed circuit board.
Printed circuit boards (PCBs) are widely used to integrate and wire electronic components. A PCB mechanically supports electronic components and electrically connects them by way of conductive tracks, pads, electrical contacts and/or other features. The tracks are typically etched from (conductive) copper layers laminated onto an isolating substrate (e.g., fiberglass, epoxy, etc.). The “FR-4” glass epoxy substrate (a mixture of glass fiber and epoxy resin) is a substrate widely used for the production of most PCBs. PCBs can involve a single substrate (single sided or double sided) or have a multi-layer structure, exhibiting outer and inner layers, to allow for higher component density. Conductors on different layers are connected with plated-through holes (vias).
The pattern of the electrical connections of a PCB is defined during production. However, sometimes a product needs be customized (for customers or an application), especially when the production volume is not important. In particular, in embedded systems, the production volume for a given application is often not substantial, yet applications require different connection schemes. In order to avoid the production of many different PCBs with only a few differences, it is desired to customize connections at post-production. After production, changes can only be made on or from the outer layers (from the exterior), for instance by cutting a trace (a flat strip of metal) or by adding a connection, either during the soldering process or by using a conductive glue, as illustrated in FIG. 2. Namely, conventionally solutions consist of soldering zero-ohm resistors, cutting a trace or adding a trace with conductive glue (FIG. 2).
As it can be realized, all of these solutions rely on an externally added (or removed) connection. When applied to inner signals, these solutions have this in common, that the signals to be connected are brought to an outer layer, as illustrated in FIG. 2.
FIG. 2 shows a cross-section of a conventional multi-layer PCB 2, comprising conductors 21-27, which notably include two inner tracks 21, 22, which are connected by respective vias 35. After production (i.e., post-production), this PCB can be customized by connecting the vias 35 from the outer, upper layer, with conductive glue 50a. 